follow path not working correct way
Your sphere object should have

location (0,0,0)

in the object panel.
The origin of the sphere should be in the center of its mesh.

You should have no other keyframed movement.  Keep this initial effort simple.
When you disable the constraint and move through timeline your sphere should have zero movement.

Consider deleting the sphere and creating a new one with the 

Follow Path constraint with the 2 [offset] keyframes

in constraint.  This should only take 88 seconds.  Perhaps you need a fresh start.